One of the standard methods for imaging a surface, particularly the surface of a semiconductor wafer, is to irradiate the surface with an electron beam in an electron microscope. Secondary electrons from the surface are collected, and may be used to form an image of the irradiated surface. Typically, in order to image the complete surface of the wafer, the electron beam is scanned across the surface, and the surface is moved orthogonally to the direction of the scanned beam.
In industrial settings it is useful to reduce the time taken to form the image. In order to do this, both the electron beam scan rate, and the movement of the surface, are typically set to be as fast as possible.
U.S. Pat. No. 4,922,106 to Berrian et al., whose disclosure is incorporated herein by reference, describes an ion beam scanning system. The system is stated to attain a selected beam current on a target object.
U.S. Patent Application 2007/0176101 to Proksch et al., whose disclosure is incorporated herein by reference, describes varying a scan rate in scanning probe instruments.
U.S. Patent Application 2007/0272857 to Hasegawa et al., whose disclosure is incorporated herein by reference, describes a scanning electron microscope which is stated to allow the user to examine conditions such as inspection speed intuitively.